If you want to do this you will need to modify $WP_ROOT$/wp-includes/feed.php :

Scroll down to “function get_the_category_rss($type = null)“

Inside that function there should be an if statement around line 315 that looks like “if ( !empty($tags) ) foreach ....“

Either comment that if statement out or delete it – all it is doing is adding the tag names as categories for it to parse when creating the categories.

Not sure if this breaks anything, but I have been testing this for a project that required a <keywords> tag in the RSS feed so I removed it from the get_the_category_rss() function and created a new function that parses the tags and adds them as keywords in the RSS feed.

Apologies for not acknowledging your reply until now. For some reason I neglected to subscribe to this topic and so didn’t get notified of any replies!

I commented out the If statement in feed.php as you suggested, which has had the desired effect. I haven’t noticed any ill effects anywhere yet. Now when I look at the feed results in IE8 the ‘Filter by Category’ option just includes the post categories and not all the tags as well.